The present invention relates to novel parathyroid hormone derivatives useful in hormone therapy.
Parathyroid hormone (PTH) is synthesized in the parathyroid, and plays an important role in controlling blood calcium concentrations or phosphoric acid ion concentrations by acting on the bone and the kidney which are its target organs. PTH is a peptide hormone consisting of 84 amino acids, and the biological activity thereof can be reproduced by a peptide fragment of an N-terminal (1 through 34 amino acid) portion [G. W. Tregear et al, Endocrinology 93, 1349-1353 (1973)].
The amino acid sequence of the peptide fragment of the N-terminal (1 through 34 amino acid ) portion of this human type PTH (this peptide fragment is hereinafter abbreviated as human PTH(1-34)) is as follows: ##STR2##
From the biological action of PTH, it is expected that the use of PTH as a drug will provide a drug useful for various bone diseases and the like. However, the following properties of the peptide are obstacles to its efficacious use as a therapeutic agent:
(1) The peptide is easily decomposed by various enzymes within the body;
(2) The absorption efficiency of the peptide into the body through various routes is very low; and
(3) The peptide is unstable to various physico-chemical conditions such as oxidation.
In order to solve such problems and understand the relationship between structure and activity of the above hormone, various derivatives have been synthesized for the PTH(1-34) fragment. While a number of syntheses have been conducted for bovine PTH(1-34), few examples are known for human PTH(1-34). For example in one such derivatives, when the C-terminus Phe of human PTH(1-34) is converted to Phe-NH.sub.2, an increase in activity is observed (Japanese Patent Unexamined Publication No. 58-96052). This increase in activity is believed to be due to inhibition of carboxypeptidase which decomposes the hormone. Further, human PTH(1-34) contains two Met residues. A molecule in which these residues are substituted with Nle residues prevents the hormone from losing its activity due to oxidation (Japanese Patent Unexamined Publication No. 61-24598).
Furthermore, F. E. Cohen et al. substituted the 3-position Ser of bovine PTH(1-34) with various L-amino acids, but the activity was markedly reduced by the amino acid substitution, except that the Ala substituted peptide exhibited an activity approximately similar to that of the natural type peptide [The Journal of Biological Chemistry 226, 1997-2004 (1991)]. S. Reppe et al. showed that for the human PTH(1-84) protein in which the 26-position Lys was substituted with Gln, the protein had an activity similar to that of the natural type protein [The Journal of Biological Chemistry 226, 14198-14201 (1991)]. As to the active human PTH(1-34) fragment, however, no derivative similarly substituted has been known.